<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>10hover</title>
    <style>
        .c1 {
            color: red;
            font-size: 18px;
        }
        .c1:hover {
            color: yellow;
            font-size: 50px;
        }

        .c2{
            height: 300px;
            width: 500px;
            border: 1px solid red;
        }
        .c2:hover{
            border: 3px solid gold;
        }

        .download{
            display: none;
        }

        .app:hover .title{
            color: red;
        }

        .app:hover .download{
            display: block;
        }
        
    </style>
</head>
<body>
<div class="c1">联通</div>
<div class="c2">电信</div>

<div class="app">
    <div class="title">下载APP</div>
    <div class="download">
        <img src="../static/erweima.png" alt="二维码图片" style="height: 450px;width: 450px;">
    </div>
</div>

</body>
</html>